The invention relates to a device which is operable to simulate the cooking state of goods, such as eggs, potatoes, rice and the like, and which allows a precise control and signaling of the cooking state to be reached. Usually, egg timers or other timers are employed for cooking e.g. eggs. The disadvantages of this method are the poor precision and the fact that the timer can only be started once the boiling temperature of the water is reached and after the egg has been immersed therein, i.e, a number of actions of the xe2x80x9cegg cookxe2x80x9d are required. Many users are overstrained by that especially if they have just tiredly fallen out of bed.
Cooking aids employing mechanical thermal models are known from various documents, e.g. EP 145 953 A2, U.S. Pat. No. 4,085,493 and EP-A 441 432. In this connection, the thermal models are simulated by appropriate materials which reproduce the thermal differential equation of the inner warming of the egg. A thermal sensor, starting a sound provider or indicating the temperature (thermometer), respectively, is then also used for indicating the cooking state. The known starting of a timer above a certain temperature is not precise either, since in this case it is necessary to wait until the water boils before the egg and the cooking aid may be immersed therein, since the influence of heating the water on the cooking state is not simulated correctly. The invention described herein avoids the disadvantages related to the principles of prior art devices.
The invention is to provide the user with a particularly simple aggregate, which simulates the cooking state very precisely and which can also be started with cold water. A number of successive controls of the cooking degree are intended to be possible without long intermediate waiting times.
According to the invention the thermal model is not simulated mechanically by material selection but by a digital computing unit making use of the differential equation (or more precise difference equation). The input of the computing model is the temperature of the cooking medium, usually water, measured with as little delay as possible. This measured value is provided by an electronic sensing device, which may be provided, for example, in the integrated circuit as a bandgap temperature sensor, or by external electric temperature sensing devices, such as a PT 100 sensing device, an iron/constantan temperature sensor, a PTC, etc.
The differential equation is provided by a digitally working model since analog circuits (RC filters) are not suitable for the long time constants for various disadvantages. The low currents and the considerable ambient temperature together with the moisture of the boiling water, sometimes even with salt, cause all kinds of electronic circuits of the analog type to become imprecise or fail. With a computing unit of digital character said disadvantages can be avoided. The precision is determined exclusively by the precision of the sensor, the AD converter and the time reference of the computing unit. Such arrangements may be produced with high precision.
The thermal differential equation of the cooking item is discretely calculated in the computing unit. In the simplest case, which matches reality quite well, it is sufficient to represent the march of temperature within the cooking item by a low pass of the first order as a xe2x80x9cdelay having a thermal time constantxe2x80x9d:
i(t)+T1dl(t)/dt=a(t)
wherein
l(t)=the inner temperature of the device
T1=the time constant of the warming of the cooking item
a(t)=the water temperature.
The differential equation is reproduced in the discretely working computing unit by a difference equation. The time constant T1 of the cooking item is detected experimentally by performing measurements with a thermometer, which is introduced into a selected cooking item (e.g. an egg), or by measuring the cooking state at a constant water temperature in certain time intervals and incorporated into the differential equation. The latter method is particularly suited for other cooking items (e.g. rice, noodles, potatoes), the temperature of which cannot be measured and which require a sensory testing (tasting the cooked food). In this case the measurements are repeated at different water temperatures in order to determine the order of the differential equation. Especially if swelling processes during cooking are important for the cooking state to be achieved (e.g. with rice or noodles), the differential equation of the first order may possibly not provide satisfactory results so that an equation of the second order will provide good results. The first time constant T1, which is greater, simulates the cooking state, wherein the second (lesser) time constant T2 simulates the swelling process. A dead time T3 may also replace the second (lesser) time constant.
A further problem which arises with prior art xe2x80x9cmechanicalxe2x80x9d thermal models is the long resetting period. A thermal model provided by mechanical means cannot be reset. In the present electronic model according to the invention the thermal time delay is reduced during cooling off. Thereby it is possible to start a new cooking process already very shortly after removing the cooking aid. This is not possible with a mechanical solution since typically the same period of time is required for cooling off as for the cooking process itself. This constitutes a great disadvantage if the person cooking the egg, after having eaten the first egg, decides that he wants to have another egg. Having to wait now makes breakfast a punishment.
As the signal provider e.g. a melody generator is used which is, however, not triggered off by means of a temperature sensor or switch, as described in EP-A A 441 432, but by the result of the computing unit. In the arrangement according to the invention the temperature sensor is located outside (i.e. quick), whereas in the prior art solutions the temperature is measure inside, i.e. delayed only.
The cooking process using the arrangement according to the invention is conceivably simple and feasible even without reading an operating manual. Take the cooking item and put it into the water together with the cooking aid. If a melody or a signal tone is heard the desired state is reached. The cooking item and the cooking aid are removed from the water. The process can now be restarted. In this connection it is irrelevant whether the water boils or is still cold at the beginning of the cooking process which constitutes a considerable simplification of operation. By means of the cooking aid it is possible, without great intellectual efforts, to make even a person who is most inexperienced in cooking a true expert of e.g. cooking eggs.
The device to be used as the cooking aid may also be used for other products than eggs. The time constant of the digital thermal model is then adapted accordingly in the program.
Furthermore, the state of the cooking degree of the cooking item, e.g. of the egg, to be achieved can be made tactilely xe2x80x9cgraspablexe2x80x9d by suitably designing the housing. A soft egg is given a soft plastic material or silicone shell. The user thus directly senses the condition the egg is supposed to have. Maloperations can thus be effectively prevented even with illiterates. The hard egg is analogously given a hard shell. The computing unit is therefore adapted to the desired cooking state (determined by the design of the jacket) and produces the appropriate signals.
Apart from the direct signaling of only one cooking state a signal generator may be integrated, which produces different signals for different cooking states. This may, for example, be one beep for soft, two beeps for medium and three beeps for hard. In this connection, the first time is determined by the digital thermal model, wherein the further times are determined by an internal timer, which triggers off further signal tones. In this way, for example, different cooking states may be signaled during cooking with one device only.
Moreover, the cooking aid may provide a signal indicating that from now on cooking with reduced supply of energy will lead to the desired result. This signal is provided for eggs upon reaching a water temperature of approx. 95xc2x0 C. (90xc2x0 C. to 100xc2x0 C.). The thermal mass of the water is then capable of completing the cooking process without any supply of energy and thus in an economical manner. For other cooking items having longer cooking times two signals may be provided. The first one upon reaching a water temperature of approx. 95xc2x0 C. and the second one approx. 5 minutes before the expected end of the cooking process. The first signal indicates that the power supply may be reduced, the second signal indicates that the process may be completed without any supply of energy.
Other cooking items may be programmed by appropriately adapting the parameters of the digital thermal model. The housings are selected such that they are unambiguously associated with the food to be cooked in pieces. This is e.g. the shape of a potato for the cooking aid for potatoes, the shape of a Chinese for the cooking aid for rice, the cooking aid for peppers is given the shape of a pepper pod and the cooking aid for milk is incorporated into a floating plastic cow. In the latter case the xe2x80x9cfood to be cooked in piecesxe2x80x9d is the device itself.